Percentages Study Guide: GED Math
Practice problems for these concepts can be found at:
Percentages are just hundredths. In this lesson, you will review how to express given percentages as both fractions and decimals. You'll find that you come into contact with percentages every day with sales tax, tips, and discounts.
Percents are everywhere you look. Go to the mall, and you'll see plenty of signs announcing "20% off" or "Take an additional 30% off." Packages at the supermarket regularly claim to include "30% more free." Even your grades for schoolwork are probably percents.
Percent is another way to represent the parts of a whole. Notice that percents are written with the percent sign after a number: 10%, 25%, 30%, 50%, 99%, and so on. The percent sign represents the words out of 100 parts or per 100 parts.
Recall that fractions represent the parts of a whole that is divided into any number of equal parts. So, you can find fractions with any whole number in the denominator: and so on. Decimals represent the parts of a whole that is divided into either 10, 100, 1,000, or another multiple of ten equal parts. Percents, by contrast, always represent a whole that is divided into 100 equal parts. That means that percents can be written as fractions with 100 in the denominator and as decimals written to the hundredths place.
Converting Percents to Decimals
Changing percents to decimals is as simple as moving the decimal point two digits to the left after removing the percent sign. Follow these basic steps:
Step 1 Drop the percent sign.
Step 2 Add a decimal point if there isn't already one. Remember that even when it's not written in, whole numbers are followed by a decimal point.
Step 3 Move the decimal point two places to the left. Add zeros if needed.
- Convert 25% to a decimal.
- Convert 2.5% to a decimal.
Drop the percent sign (25% becomes 25).
Add a decimal point: 25.
Move the decimal point two places to the left and add a leading zero: 0.25
25% = 0.25
Drop the percent sign (2.5% becomes 2.5). There is already a decimal point, so move the decimal point two digits to the left. Doing this requires a zero as a placeholder in the tenths place. Also add a leading zero to the left of the decimal point: 0.025.
2.5% = 0.025
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